In many agricultural and industrial off-road equipment, a priority valve is used in a power on demand system to assure that a priority function, such as steering, always has available fluid. In such systems, sould the wheel encounter a curb or rut wherein the priority function demands a greater pressure than the pump can supply, it is usual that the priority function will stall. When this happens, the pressure differential across the priority valve becomes zero causing the priority valve to shut off flow to secondary or non-priority functions. The current practice for remedying this problem is to provide a pilot line relief valve and an orifice pilot flow for the spring chamber. The relief valve is set above the maximum pressure requirement for the priority function but below maximum pump pressure. However the relief valve and orifice pilot flow suffer disadvantages in that there is added noise, added power loss at stall, and in case of some steering applications, continued slow steering wheel rotation during stall or when in a lock position.
Now a priority valve has been invented which eliminates the need for the orifice pilot and relief valve.